1. Field of the Invention
The present invention relates to a method for forming bumps on the electrodes of semiconductor devices.
2. Prior Art
Bumps are generally formed on electrodes of semiconductor devices by a wire bonding apparatus. When such bumps (which are connected to, for instance, terminals) are made out of a wire, it is important to cut the wire consistently at the same position. Various methods have been proposed for this purpose. However, all of these methods have respective advantages and disadvantages. The method disclosed in, for instance, Japanese Patent Application Publication (Kokoku) No. 6-95519 is for cutting wire at consistently the same position, and this method is shown FIG. 2.
In step (a) of FIG. 2, with a clamper 3 closed, a ball 6 is formed by an electrical discharge on the tip end of a wire 5 which passes through a capillary 4. Then, the clamper 3 is opened, and the capillary is lowered so that the ball 6 is pressed against the surface of an electrode 2 on a semiconductor device 1 as shown in step (b).
After this, the capillary is raised as shown in step (c); and a cutting jig 11 which has a sharp edge 10 advances so that a cut 7 is formed at the root of the ball 6.
When the cut 7 has thus ben made, the cutting jig 11 withdraws; and at the same time, the clamper 3 is closed to hold the wire 5, and the clamper 3 and capillary 4 are both raised in step (d). As a result, the wire 5 breaks at the cut 7, so that a bump 8 is formed on the electrode 2.
Next, a pressing member 12 is caused to advance horizontally as shown in step (e) and is then lowered so that a prescribed pressure is applied to the bump 8 in step (f). As a result, the upper surface of the bump 8 is formed into a flattened portion 9 by the pressing member 12 in step (g).
In the prior art described above, the cut 7 is formed from one side (right side in FIG. 2) by the cutting jig 11. As a result, the portion of the wire 5 above the cut 7 can be easily deformed. Furthermore, so as to form the flattened portion 9 on the bump 8 following breaking of the wire, operating time is required in order to advance and then lower the pressing member 12. Moreover, a means for operating the pressing member 12 is required, thus making the apparatus more complicated.